-0.1111

To find the value of this expression, first convert the mixed number to an improper fraction:

8 6/9 = (9*8 + 6)/9 = 78/9

Now, subtract 9:

78/9 - 9 = 78/9 - 81/9 = (78 - 81)/9 = -3/9 = -1/3

Therefore, the value of the expression is -1/3 or approximately -0.1111.